Background: Until recently, few genomic reagents specific for non-human primate research have been available. To address this need, we have constructed a macaque-specific high-density oligonucleotide microarray by using highly fragmented low-pass sequence contigs from the rhesus genome project together with the detailed sequence and exon structure of the human genome. Using this method, we designed oligonucleotide probes to over 17,000 distinct rhesus/human gene orthologs and increased by four-fold the number of available genes relative to our firstgeneration expressed sequence tag (EST)-derived array.
Results: We constructed a database containing 248,000 exon sequences from 23,000 human RefSeq genes and
compared each human exon with its best matching sequence in the January 2005 version of the rhesus genome project list of 486,000 DNA contigs. Best matching rhesus exon sequences for each of the 23,000 human genes were then concatenated in the proper order and orientation to produce a rhesus "virtual transcriptome." Microarray probes were designed, one per gene, to the region closest to the 3' untranslated region (UTR) of each rhesus virtual transcript. Each probe was compared to a composite rhesus/human transcript database to test for cross-hybridization potential yielding a final probe set representing 18,296 rhesus/human gene orthologs, including
transcript variants, and over 17,000 distinct genes. We hybridized mRNA from rhesus brain and spleen to both the EST- and genome-derived microarrays. Besides four-fold greater gene coverage, the genome-derived array also showed greater mean signal intensities for genes present on both arrays. Genome-derived probes showed 99.4% identity when compared to 4,767 rhesus GenBank sequence tag site (STS) sequences indicating that early stage lowpass
versions of complex genomes are of sufficient quality to yield valuable functional genomic information when
combined with finished genome information from a closely related species.
Conclusion: The number of different genes represented on microarrays for unfinished genomes can be greatly
increased by matching known gene transcript annotations from a closely related species with sequence data from
the unfinished genome. Signal intensity on both EST- and genome-derived arrays was highly correlated with probe
distance from the 3' UTR, information often missing from ESTs yet present in early-stage genome projects.

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Public Health Service grants R24 RR016354 and P51 RR000166 from the National Center for Research Resources.